Method of oligonucleotide synthesis

ABSTRACT

Methods and kits for synthesizing a plurality of oligonucleotides are provided. Methods for providing a plurality of oligonucleotides enriched for full length oligonucleotides are provided. Truncated oligonucleotides are preferentially removed from the sample by digestion. Methods are also provided for amplification of a plurality of oligonucleotides.

This application is a continuation of U.S. patent application Ser. No.10/741,068, filed Dec. 19, 2003 which is incorporated by reference forall purposes.

FIELD OF THE INVENTION

The methods of the invention relate generally to synthesis of aplurality of oligonucleotide sequences. The methods provide forenriching a plurality of synthesized oligonucleotides that comprisestruncated and full length oligonucleotides for full lengtholigonucleotides. Methods for amplification of full lengtholigonucleotides in the enriched sample are also disclosed.

BACKGROUND OF THE INVENTION

Synthesis of large numbers of different oligonucleotide sequences onsolid supports has been described previously, see for example, Fodor etal., Science 251(4995), 767-73, 1991, Fodor et al., Nature 364(6437),555-6, 1993 and Pease et al. PNAS USA 91(11), 5022-6, 1994 and U.S. Pat.No. 5,445,934.

SUMMARY OF THE INVENTION

In one embodiment a method of making a plurality of oligonucleotidesthat is enriched for full length oligonucleotides is disclosed. Aplurality of oligonucleotides is synthesized on a solid support so thatthe oligonucleotides are attached to the solid support by a cleavablelinker, for example uracil, and the 5′ end of the full lengtholigonucleotides includes an element that confers nuclease resistance,for example, phosphorothioate linkages. After cleaving the linker torelease the oligonucleotides from the solid support, a primer ishybridized to the 3′ end of the released oligonucleotides and extendedto generate double stranded oligonucleotides. Truncated oligonucleotidesare then digested, for example, by adding a 5′ to 3′ exonuclease such asT7 gene 6 exonuclease. The oligonucleotides that are at least aspecified length, full length oligonucleotide, are resistant todigestion because they include the nuclease resistant element. Afterdigestion the sample is enriched for full length oligonucleotides. In apreferred embodiment more than 1000 different sequence oligonucleotidesare synthesized simultaneously.

In a preferred embodiment four phosphorothioate linkages areincorporated into the 5′ end of the oligonucleotide, resulting innuclease resistance.

In another embodiment a method of amplifying a plurality of sequences ofinterest is disclosed. A plurality of template oligonucleotides issynthesized on a solid support. The template oligonucleotides areattached to the solid support by a cleavable linker and the full lengthtemplate oligonucleotides include a 5′ element that confers nucleaseresistance. The cleavable linker is cleaved to release the templateoligonucleotides from the solid support. A primer is hybridized to the3′ end of the released template oligonucleotides and extended to makethe template oligonucleotides double stranded. In a preferred embodimentoligonucleotides that are not full length are digested with anexonuclease. The double stranded template oligonucleotides are nickednear the 5′ end of one strand, thereby generating a 5′ and a 3′ portionof one strand, wherein the 3′ portion comprises a sequence of interest,and the 5′ portion is extended with a strand displacing enzyme whereinthe 3′ portion is released and a new copy of the 3′ portion issynthesized.

In a preferred embodiment the method may be used to amplify at least1000 different sequences of interest. Each sequence of interest mayinclude a common adaptor sequence and a locus specific sequence. Nickingmay be by a nicking restriction enzyme, such as BstNB1. In anotherembodiment one strand of the double stranded oligonucleotide may beblocked from cleavage, for example by a phosphorothioate linkage, andthe nicking may be by a restriction enzyme that cleaves double strandednucleic acid. In a preferred embodiment cleavage and extension takeplace in the same reaction and are preferably repeated multiple times,releasing the 3′ portion each time, thereby amplifying the 3′ portion.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows synthesis of a mixture of full length and truncatedoligonucleotides on a solid support. Truncated species are digestedleaving primarily full length oligonucleotides.

FIG. 2 shows amplification of full length oligonucleotides using anicking enzyme and strand displacement.

FIG. 3 shows a template oligonucleotide (100) and the amplificationproduct (107) resulting from amplification using the method shown inFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A) General

The present invention has many preferred embodiments and relies on manypatents, applications and other references for details known to those ofthe art. Therefore, when a patent, application, or other reference iscited or repeated below, it should be understood that it is incorporatedby reference in its entirety for all purposes as well as for theproposition that is recited.

As used in this application, the singular form “a,” “an,” and “the”include plural references unless the context clearly dictates otherwise.For example, the term “an agent” includes a plurality of agents,including mixtures thereof.

An individual is not limited to a human being but may also be otherorganisms including but not limited to mammals, plants, bacteria, orcells derived from any of the above.

Throughout this disclosure, various aspects of this invention can bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

The practice of the present invention may employ, unless otherwiseindicated, conventional techniques and descriptions of organicchemistry, polymer technology, molecular biology (including recombinanttechniques), cell biology, biochemistry, and immunology, which arewithin the skill of the art. Such conventional techniques includepolymer array synthesis, hybridization, ligation, and detection ofhybridization using a label. Specific illustrations of suitabletechniques can be had by reference to the example herein below. However,other equivalent conventional procedures can, of course, also be used.Such conventional techniques and descriptions can be found in standardlaboratory manuals such as Genome Analysis: A Laboratory Manual Series(Vols. I-IV), Using Antibodies: A Laboratory Manual, Cells: A LaboratoryManual, PCR Primer: A Laboratory Manual, and Molecular Cloning: ALaboratory Manual (all from Cold Spring Harbor Laboratory Press),Stryer, L. (1995) Biochemistry (4th Ed.) Freeman, New York, Gait,“Oligonucleotide Synthesis: A Practical Approach” 1984, IRL Press,London, Nelson and Cox (2000), Lehninger, Principles of Biochemistry3^(rd) Ed., W.H. Freeman Pub., New York, N.Y. and Berg et al. (2002)Biochemistry, 5^(th) Ed., W.H. Freeman Pub., New York, N.Y., all ofwhich are herein incorporated in their entirety by reference for allpurposes.

The present invention can employ solid substrates, including arrays insome preferred embodiments. Methods and techniques applicable to polymer(including protein) array synthesis have been described in U.S. Ser. No.09/536,841, WO 00/58516, U.S. Pat. Nos. 5,143,854, 5,242,974, 5,252,743,5,324,633, 5,384,261, 5,405,783, 5,424,186, 5,451,683, 5,482,867,5,491,074, 5,527,681, 5,550,215, 5,571,639, 5,578,832, 5,593,839,5,599,695, 5,624,711, 5,631,734, 5,795,716, 5,831,070, 5,837,832,5,856,101, 5,858,659, 5,936,324, 5,968,740, 5,974,164, 5,981,185,5,981,956, 6,025,601, 6,033,860, 6,040,193, 6,090,555, 6,136,269,6,269,846 and 6,428,752, in PCT Applications Nos. PCT/US99/00730(International Publication Number WO 99/36760) and PCT/US01/04285, whichare all incorporated herein by reference in their entirety for allpurposes.

Patents that describe synthesis techniques in specific embodimentsinclude U.S. Pat. Nos. 5,412,087, 6,147,205, 6,262,216, 6,310,189,5,889,165, and 5,959,098. Nucleic acid arrays are described in many ofthe above patents, but the same techniques are applied to polypeptidearrays.

Nucleic acid arrays that are useful in the present invention includethose that are commercially available from Affymetrix (Santa Clara,Calif.) under the brand name GeneChip®. Example arrays are shown on thewebsite at affymetrix.com.

The present invention also contemplates many uses for polymers attachedto solid substrates. These uses include gene expression monitoring,profiling, library screening, genotyping and diagnostics. Geneexpression monitoring, and profiling methods can be shown in U.S. Pat.Nos. 5,800,992, 6,013,449, 6,020,135, 6,033,860, 6,040,138, 6,177,248and 6,309,822. Genotyping and uses thereof are shown in U.S. Ser. Nos.60/319,253, 10/013,598, and U.S. Pat. Nos. 5,856,092, 6,300,063,5,858,659, 6,284,460, 6,361,947, 6,368,799 and 6,333,179. Other uses areembodied in U.S. Pat. Nos. 5,871,928, 5,902,723, 6,045,996, 5,541,061,and 6,197,506.

The present invention also contemplates sample preparation methods incertain preferred embodiments. Prior to or concurrent with genotyping,the genomic sample may be amplified by a variety of mechanisms, some ofwhich may employ PCR. See, e.g., PCR Technology: Principles andApplications for DNA Amplification (Ed. H. A. Erlich, Freeman Press, NY,N.Y., 1992); PCR Protocols: A Guide to Methods and Applications (Eds.Innis, et al., Academic Press, San Diego, Calif., 1990); Mattila et al.,Nucleic Acids Res. 19, 4967 (1991); Eckert et al., PCR Methods andApplications 1, 17 (1991); PCR (Eds. McPherson et al., IRL Press,Oxford); and U.S. Pat. Nos. 4,683,202, 4,683,195, 4,800,159 4,965,188,and 5,333,675, and each of which is incorporated herein by reference intheir entireties for all purposes. The sample may be amplified on thearray. See, for example, U.S. Pat. No. 6,300,070 and U.S. Ser. No.09/513,300, which are incorporated herein by reference.

Other suitable amplification methods include the ligase chain reaction(LCR) (e.g., Wu and Wallace, Genomics 4, 560 (1989), Landegren et al.,Science 241, 1077 (1988) and Barringer et al. Gene 89:117 (1990)),transcription amplification (Kwoh et al., Proc. Natl. Acad. Sci. USA 86,1173 (1989) and WO88/10315), self-sustained sequence replication(Guatelli et al., Proc. Nat. Acad. Sci. USA, 87, 1874 (1990) andWO90/06995), selective amplification of target polynucleotide sequences(U.S. Pat. No. 6,410,276), consensus sequence primed polymerase chainreaction (CP-PCR) (U.S. Pat. No. 4,437,975), arbitrarily primedpolymerase chain reaction (AP-PCR) (U.S. Pat. Nos. 5,413,909, 5,861,245)and nucleic acid based sequence amplification (NABSA). (See, U.S. Pat.Nos. 5,409,818, 5,554,517, and 6,063,603, each of which is incorporatedherein by reference). Other amplification methods that may be used aredescribed in, U.S. Pat. Nos. 5,242,794, 5,494,810, 4,988,617 and in U.S.Ser. No. 09/854,317, each of which is incorporated herein by reference.

Additional methods of sample preparation and techniques for reducing thecomplexity of a nucleic sample are described in Dong et al., GenomeResearch 11, 1418 (2001), in U.S. Pat. Nos. 6,361,947, 6,391,592 andU.S. Ser. Nos. 09/916,135, 09/920,491, 09/910,292, and 10/013,598.

Methods for conducting polynucleotide hybridization assays have beenwell developed in the art. Hybridization assay procedures and conditionswill vary depending on the application and are selected in accordancewith the general binding methods known including those referred to in:Maniatis et al. Molecular Cloning: A Laboratory Manual (2^(nd) Ed. ColdSpring Harbor, N.Y., 1989); Berger and Kimmel Methods in Enzymology,Vol. 152, Guide to Molecular Cloning Techniques (Academic Press, Inc.,San Diego, Calif., 1987); Young and Davism, P.N.A.S, 80: 1194 (1983).Methods and apparatus for carrying out repeated and controlledhybridization reactions have been described in U.S. Pat. Nos. 5,871,928,5,874,219, 6,045,996 and 6,386,749, 6,391,623 each of which areincorporated herein by reference

The present invention also contemplates signal detection ofhybridization between ligands in certain preferred embodiments. See U.S.Pat. Nos. 5,143,854, 5,578,832; 5,631,734; 5,834,758; 5,936,324;5,981,956; 6,025,601; 6,141,096; 6,185,030; 6,201,639; 6,218,803; and6,225,625, in U.S. Ser. No. 60/364,731 and in PCT ApplicationPCT/US99/06097 (published as WO99/47964), each of which also is herebyincorporated by reference in its entirety for all purposes.

Methods and apparatus for signal detection and processing of intensitydata are disclosed in, for example, U.S. Pat. Nos. 5,143,854, 5,547,839,5,578,832, 5,631,734, 5,800,992, 5,834,758; 5,856,092, 5,902,723,5,936,324, 5,981,956, 6,025,601, 6,090,555, 6,141,096, 6,185,030,6,201,639; 6,218,803; and 6,225,625, in U.S. Ser. No. 60/364,731 and inPCT Application PCT/US99/06097 (published as WO99/47964), each of whichalso is hereby incorporated by reference in its entirety for allpurposes.

The practice of the present invention may also employ conventionalbiology methods, software and systems. Computer software products of theinvention typically include computer readable medium havingcomputer-executable instructions for performing the logic steps of themethod of the invention. Suitable computer readable medium includefloppy disk, CD-ROM/DVD/DVD-ROM, hard-disk drive, flash memory, ROM/RAM,magnetic tapes and etc. The computer executable instructions may bewritten in a suitable computer language or combination of severallanguages. Basic computational biology methods are described in, e.g.Setubal and Meidanis et al., Introduction to Computational BiologyMethods (PWS Publishing Company, Boston, 1997); Salzberg, Searles,Kasif, (Ed.), Computational Methods in Molecular Biology, (Elsevier,Amsterdam, 1998); Rashidi and Buehler, Bioinformatics Basics:Application in Biological Science and Medicine (CRC Press, London, 2000)and Ouelette and Bzevanis Bioinformatics: A Practical Guide for Analysisof Gene and Proteins (Wiley & Sons, Inc., 2^(nd) ed., 2001). See U.S.Pat. No. 6,420,108.

The present invention may also make use of various computer programproducts and software for a variety of purposes, such as probe design,management of data, analysis, and instrument operation. See, U.S. Pat.Nos. 5,593,839, 5,795,716, 5,733,729, 5,974,164, 6,066,454, 6,090,555,6,185,561, 6,188,783, 6,223,127, 6,229,911 and 6,308,170.

Additionally, the present invention may have preferred embodiments thatinclude methods for providing genetic information over networks such asthe Internet as shown in U.S. Ser. No. 10/063,559 (United StatesPublication No. US20020183936), 60/349,546, 60/376,003, 60/394,574 and60/403,381.

B) Definitions

An “array” is an intentionally created collection of molecules which canbe prepared either synthetically or biosynthetically. The molecules inthe array can be identical or different from each other. The array canassume a variety of formats, e.g., libraries of soluble molecules;libraries of compounds tethered to resin beads, silica chips, or othersolid supports.

“Biopolymer” or “biological polymer” is intended to mean repeating unitsof biological or chemical moieties. Representative biopolymers include,but are not limited to, nucleic acids, oligonucleotides, amino acids,proteins, peptides, hormones, oligosaccharides, lipids, glycolipids,lipopolysaccharides, phospholipids, synthetic analogues of theforegoing, including, but not limited to, inverted nucleotides, peptidenucleic acids, Meta-DNA, and combinations of the above. “Biopolymersynthesis” is intended to encompass the synthetic production, bothorganic and inorganic, of a biopolymer.

“Complementary” or “substantially complementary” refers to thehybridization or base pairing between nucleotides or nucleic acids, suchas, for instance, between the two strands of a double stranded DNAmolecule or between an oligonucleotide primer and a primer binding siteon a single stranded nucleic acid to be sequenced or amplified.Complementary nucleotides are, generally, A and T (or A and U), or C andG. Two single stranded RNA or DNA molecules are said to be substantiallycomplementary when the nucleotides of one strand, optimally aligned andcompared and with appropriate nucleotide insertions or deletions, pairwith at least about 80% of the nucleotides of the other strand, usuallyat least about 90% to 95%, and more preferably from about 98 to 100%.Alternatively, substantial complementary exists when an RNA or DNAstrand will hybridize under selective hybridization conditions to itscomplement. Typically, selective hybridization will occur when there isat least about 65% complementary over a stretch of at least 14 to 25nucleotides, preferably at least about 75%, more preferably at leastabout 90% complementary. See, M. Kanehisa Nucleic Acids Res. 12:203(1984), incorporated herein by reference.

A “combinatorial synthesis strategy” is an ordered strategy for parallelsynthesis of diverse polymer sequences by sequential addition ofreagents which may be represented by a reactant matrix and a switchmatrix, the product of which is a product matrix. A reactant matrix is al column by m row matrix of the building blocks to be added. The switchmatrix is all or a subset of the binary numbers, preferably ordered,between l and m arranged in columns. A “binary strategy” is one in whichat least two successive steps illuminate a portion, often half, of aregion of interest on the substrate. In a binary synthesis strategy, allpossible compounds which can be formed from an ordered set of reactantsare formed. In most preferred embodiments, binary synthesis refers to asynthesis strategy which also factors a previous addition step. Forexample, a strategy in which a switch matrix for a masking strategyhalves regions that were previously illuminated, illuminating about halfof the previously illuminated region and protecting the remaining half(while also protecting about half of previously protected regions andilluminating about half of previously protected regions). It will berecognized that binary rounds may be interspersed with non-binary roundsand that only a portion of a substrate may be subjected to a binaryscheme. A combinatorial “masking” strategy is a synthesis which useslight or other spatially selective deprotecting or activating agents toremove protecting groups from materials for addition of other materialssuch as amino acids.

“Effective amount” refers to an amount sufficient to induce a desiredresult.

“Genome” is all the genetic material in the chromosomes of an organism.DNA derived from the genetic material in the chromosomes of a particularorganism is genomic DNA. A genomic library is a collection of clonesmade from a set of randomly generated overlapping DNA fragmentsrepresenting the entire genome of an organism.

Hybridization conditions will typically include salt concentrations ofless than about 1M, more usually less than about 500 mM and preferablyless than about 200 mM. Hybridization temperatures can be as low as 5°C., but are typically greater than 22° C., more typically greater thanabout 30° C., and preferably in excess of about 37° C. Longer fragmentsmay require higher hybridization temperatures for specifichybridization. As other factors may affect the stringency ofhybridization, including base composition and length of thecomplementary strands, presence of organic solvents and extent of basemismatching, the combination of parameters is more important than theabsolute measure of any one alone.

Hybridizations are usually performed under stringent conditions, forexample, at a salt concentration of no more than 1 M and a temperatureof at least 25° C. For example, conditions of 5×SSPE (750 mM NaCl, 50 mMNaPhosphate, 5 mM EDTA, pH 7.4) and a temperature of 25-30° C. aresuitable for allele-specific probe hybridizations. For stringentconditions, see, for example, Sambrook, Fritsche and Maniatis.“Molecular Cloning A laboratory Manual” 2^(nd) Ed. Cold Spring HarborPress (1989) which is hereby incorporated by reference in its entiretyfor all purposes above.

The term “hybridization” refers to the process in which twosingle-stranded polynucleotides bind non-covalently to form a stabledouble-stranded polynucleotide; triple-stranded hybridization is alsotheoretically possible. The resulting (usually) double-strandedpolynucleotide is a “hybrid.” The proportion of the population ofpolynucleotides that forms stable hybrids is referred to herein as the“degree of hybridization.”

“Hybridization probes” are oligonucleotides capable of binding in abase-specific manner to a complementary strand of nucleic acid. Suchprobes include peptide nucleic acids, as described in Nielsen et al.,Science 254, 1497-1500 (1991), and other nucleic acid analogs andnucleic acid mimetics. See U.S. Pat. No. 6,156,501.

“Hybridizing specifically to” refers to the binding, duplexing, orhybridizing of a molecule substantially to, or only to, a particularnucleotide sequence or sequences under stringent conditions when thatsequence is present in a complex mixture (e.g., total cellular DNA orRNA).

“Isolated nucleic acid” is an object species that is the predominantspecies present (i.e., on a molar basis it is more abundant than anyother individual species in the composition). Preferably, an isolatednucleic acid comprises at least about 50, 80 or 90% (on a molar basis)of all macromolecular species present. Most preferably, the objectspecies is purified to essential homogeneity (contaminant species cannotbe detected in the composition by conventional detection methods).

“Mixed population” or “complex population” refers to any samplecontaining both desired and undesired nucleic acids. As a non-limitingexample, a complex population of nucleic acids may be total genomic DNA,total genomic RNA or a combination thereof. Moreover, a complexpopulation of nucleic acids may have been enriched for a givenpopulation but include other undesirable populations. For example, acomplex population of nucleic acids may be a sample which has beenenriched for desired messenger RNA (mRNA) sequences but still includessome undesired ribosomal RNA sequences (rRNA).

“Monomer” refers to any member of the set of molecules that can bejoined together to form an oligomer or polymer. The set of monomersuseful in the present invention includes, but is not restricted to, forthe example of (poly)peptide synthesis, the set of L-amino acids,D-amino acids, or synthetic amino acids. As used herein, “monomer”refers to any member of a basis set for synthesis of an oligomer. Forexample, dimers of L-amino acids form a basis set of 400 “monomers” forsynthesis of polypeptides. Different basis sets of monomers may be usedat successive steps in the synthesis of a polymer. The term “monomer”also refers to a chemical subunit that can be combined with a differentchemical subunit to form a compound larger than either subunit alone.

Nucleic acids according to the present invention may include any polymeror oligomer of pyrimidine and purine bases, preferably cytosine,thymine, and uracil, and adenine and guanine, respectively. See AlbertL. Lehninger, PRINCIPLES OF BIOCHEMISTRY, at 793-800 (Worth Pub. 1982).Indeed, the present invention contemplates any deoxyribonucleotide,ribonucleotide or peptide nucleic acid component, and any chemicalvariants thereof, such as methylated, hydroxymethylated or glucosylatedforms of these bases, and the like. The polymers or oligomers may beheterogeneous or homogeneous in composition, and may be isolated fromnaturally-occurring sources or may be artificially or syntheticallyproduced. In addition, the nucleic acids may be DNA or RNA, or a mixturethereof, and may exist permanently or transitionally in single-strandedor double-stranded form, including homoduplex, heteroduplex, and hybridstates.

An “oligonucleotide” or “polynucleotide” is a nucleic acid ranging fromat least 2, preferable at least 8, and more preferably at least 20nucleotides in length or a compound that specifically hybridizes to apolynucleotide. Polynucleotides of the present invention includesequences of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) whichmay be isolated from natural sources, recombinantly produced orartificially synthesized and mimetics thereof. A further example of apolynucleotide of the present invention may be peptide nucleic acid(PNA). The invention also encompasses situations in which there is anontraditional base pairing such as Hoogsteen base pairing which hasbeen identified in certain tRNA molecules and postulated to exist in atriple helix. “Polynucleotide” and “oligonucleotide” are usedinterchangeably in this application.

Oligonucleotides may include modifications. Amino modifier reagents maybe used to introduce a primary amino group into the oligo. A primaryamino group is useful for a variety of coupling reactions that can beused to attach various labels to the oligo. The most frequently usedlabels are in the form of NHS-esters, which can couple with primaryamino groups. A variety of derivatives of biotin are available in whichthe biotin moiety is connected (through the 4-carboxybutyl group) to alinker molecule that can be attached directly to an oligonucleotide.Fluorescent dies such as 6-FAM, HEX, TET, TAMRA, and ROX may be coupledto an oligo. Phosphate groups may be attached to the 5′ and/or 3′ end ofan oligo. Oligos may also be phosphorothioated. A phosphorothioate groupis a modified phosphate group with one of the oxygen atoms replaced by asulfur atom. In a phosphorothioated oligo (often called an “S-Oligo”),some or all of the internucleotide phosphate groups are replaced byphosphorothioate groups. The modified “backbone” of an S-Oligo isresistant to the action of most exonucleases and endonucleases. In someembodiments the oligo is sulfurized only at the last few residues ateach end of the oligo. This results in an oligo that is resistent toexonucleases, but has a natural DNA center. Degenerate bases may also beincorporated into an oligo. may also be incorporated into an oligoAdditional modifications that are available include, for example,2′O-Methyl RNA, 3′-Glyceryl, 3′-Terminators, Acrydite, Cholesterollabeling, Dabcyl, Digoxigenin labeling, Methylated nucleosides, SpacerReagents, Thiol Modifications DeoxyInosine, DeoxyUridine and halogenatednucleosides.

A “probe” is a surface-immobilized molecule that can be recognized by aparticular target. Examples of probes that can be investigated by thisinvention include, but are not restricted to, agonists and antagonistsfor cell membrane receptors, toxins and venoms, viral epitopes, hormones(e.g., opioid peptides, steroids, etc.), hormone receptors, peptides,enzymes, enzyme substrates, cofactors, drugs, lectins, sugars,oligonucleotides, nucleic acids, oligosaccharides, proteins, andmonoclonal antibodies. See U.S. Pat. No. 6,582,908 for an example ofarrays having all possible combinations of probes with 10, 12, and morebases.

“Primer” is a single-stranded oligonucleotide capable of acting as apoint of initiation for template-directed DNA synthesis under suitableconditions e.g., buffer and temperature, in the presence of fourdifferent nucleoside triphosphates and an agent for polymerization, suchas, for example, DNA or RNA polymerase or reverse transcriptase. Thelength of the primer, in any given case, depends on, for example, theintended use of the primer, and generally ranges from 15 to 30nucleotides. Short primer molecules generally require coolertemperatures to form sufficiently stable hybrid complexes with thetemplate. A primer need not reflect the exact sequence of the templatebut must be sufficiently complementary to hybridize with such template.The primer site is the area of the template to which a primerhybridizes. The primer pair is a set of primers including a 5′ upstreamprimer that hybridizes with the 5′ end of the sequence to be amplifiedand a 3′ downstream primer that hybridizes with the complement of the 3′end of the sequence to be amplified.

A “tag” or “tag sequence” is a selected nucleic acid with a specifiednucleic acid sequence. A tag probe has a region that is complementary toa selected tag. A set of tags or a collection of tags is a collection ofspecified nucleic acids that may be of similar length and similarhybridization properties, for example similar T_(m). The tags in acollection of tags bind to tag probes with minimal cross hybridizationso that a single species of tag in the tag set accounts for the majorityof tags which bind to a given tag probe species under hybridizationconditions. For additional description of tags and tag probes andmethods of selecting tags and tag probes see U.S. Ser. No. 08/626,285and EP/0799897, each of which is incorporated herein by reference intheir entirety.

“Solid support”, “support”, and “substrate” are used interchangeably andrefer to a material or group of materials having a rigid or semi-rigidsurface or surfaces. In many embodiments, at least one surface of thesolid support will be substantially flat, although in some embodimentsit may be desirable to physically separate synthesis regions fordifferent compounds with, for example, wells, raised regions, pins,etched trenches, or the like. According to other embodiments, the solidsupport(s) will take the form of beads, resins, gels, microspheres, orother geometric configurations. See U.S. Pat. No. 5,744,305 forexemplary substrates.

A “target” is a molecule that has an affinity for a given probe. Targetsmay be naturally-occurring or man-made molecules. Also, they can beemployed in their unaltered state or as aggregates with other species.Targets may be attached, covalently or noncovalently, to a bindingmember, either directly or via a specific binding substance. Examples oftargets which can be employed by this invention include, but are notrestricted to, antibodies, cell membrane receptors, monoclonalantibodies and antisera reactive with specific antigenic determinants(such as on viruses, cells or other materials), drugs, oligonucleotides,nucleic acids, peptides, cofactors, lectins, sugars, polysaccharides,cells, cellular membranes, and organelles. Targets are sometimesreferred to in the art as anti-probes. As the term targets is usedherein, no difference in meaning is intended. A “Probe Target Pair” isformed when two macromolecules have combined through molecularrecognition to form a complex.

“Restriction enzyme or endonuclease” A number of methods disclosedherein require the use of restriction enzymes to fragment the nucleicacid sample. In general, a restriction enzyme recognizes a specificnucleotide sequence of four to eight nucleotides and cuts the DNA at asite within or a specific distance from the recognition sequence. Forexample, the restriction enzyme EcoRI recognizes the sequence GAATTC andwill cut a DNA molecule between the G and the first A. The length of therecognition sequence is roughly proportional to the frequency ofoccurrence of the site in the genome. A simplistic theoretical estimateis that a six base pair recognition sequence will occur once in every4096 (4⁶) base pairs while a four base pair recognition sequence willoccur once every 256 (4⁴) base pairs. In silico digestions of sequencesfrom the Human Genome Project show that the actual occurrences may bemore or less frequent, depending on the sequence of the restrictionsite. Because the restriction sites are rare, the appearance of shorterrestriction fragments, for example those less than 1000 base pairs, ismuch less frequent than the appearance of longer fragments. Manydifferent restriction enzymes are known and appropriate restrictionenzymes can be selected for a desired result. (For a description of manyrestriction enzymes see, New England BioLabs Catalog which is hereinincorporated by reference in its entirety for all purposes).

“Nicking endonucleases” are restriction enzymes that hydrolyze only onestrand of the DNA duplex, to produce DNA molecules that are “nicked”,rather than cleaved. The resulting nicks (3′-hydroxyl, 5′-phosphate) canserve as initiation points for further enzymatic reactions such asreplacement DNA synthesis, strand-displacement amplification (Walker, G.T. et al. (1992) Proc. Natl. Acad. Sci. USA 89, 392-396.),exonucleolytic degradation or the creation of small gaps (Wang, H. andHays, J. B. (2000) Mol. Biotechnol. 15, 97-104). These enzymes may occurnaturally or they may be engineered or altered to nick. N.BstNB I occursnaturally and nicks because it is unable to form dimers. N.Alw I is aderivative of the restriction enzyme Alw I, that has been engineered tobehave in the same way. These enzymes nick adjacent to their recognitionsequences. N.BbvC IA and N.BbvC IB are derived from the heterodimericrestriction enzyme BbvC I, each has only one catalytic site so they nickwithin the recognition sequence but on opposite strands. In someembodiments newly engineered or discovered nicking enzymes are used. Itis likely that the methods used to engineer existing nicking enzymeswill be broadly applicable and many existing restriction enzymes may beengineered to produce corresponding nicking enzymes.

DNA Polymerase I Large (Klenow) Fragment consists of a singlepolypeptide chain (68 kDa) that lacks the 5′→3′ exonuclease activity ofintact E. coli DNA polymerase I, but retains its 5′→3′ polymerase, 3′→5′exonuclease and strand displacement activities. The Klenow fragment hasbeen used for strand displacement amplification (SDA). See, e.g., U.S.Pat. Nos. 6,379,888; 6,054,279; 5,919,630; 5,856,145; 5,846,726;5,800,989; 5,766,852; 5,744,311; 5,736,365; 5,712,124; 5,702,926;5,648,211; 5,641,633; 5,624,825; 5,593,867; 5,561,044; 5,550,025;5,547,861; 5,536,649; 5,470,723; 5,455,166; 5,422,252; 5,270,184, allincorporated herein by reference. Phi29 (φ29) polymerase may also beused for strand displacement amplification. See, for example, U.S. Pat.Nos. 5,576,204, 5,854,033, 5,198,543, 5,001,050, 6,280,949 and6,642,034.

“Adaptor sequences” or “adaptors” are generally oligonucleotides of atleast 5, 10, or 15 bases and preferably no more than 50 or 60 bases inlength; however, they may be even longer, up to 100 or 200 bases.Adaptor sequences may be synthesized using any methods known to those ofskill in the art. For the purposes of this invention they may, asoptions, comprise primer binding sites, recognition sites forendonucleases, common sequences and promoters. The adaptor may beentirely or substantially double stranded. A double stranded adaptor maycomprise two oligonucleotides that are at least partially complementary.The adaptor may be phosphorylated or unphosphorylated on one or bothstrands. Adaptors may be more efficiently ligated to fragments if theycomprise a substantially double stranded region and a short singlestranded region which is complementary to the single stranded regioncreated by digestion with a restriction enzyme. For example, when DNA isdigested with the restriction enzyme EcoRI the resulting double strandedfragments are flanked at either end by the single stranded overhang5′-AATT-3′, an adaptor that carries a single stranded overhang5′-AATT-3′ will hybridize to the fragment through complementaritybetween the overhanging regions. This “sticky end” hybridization of theadaptor to the fragment may facilitate ligation of the adaptor to thefragment but blunt ended ligation is also possible. Blunt ends can beconverted to sticky ends using the exonuclease activity of the Klenowfragment. For example when DNA is digested with PvuII the blunt ends canbe converted to a two base pair overhang by incubating the fragmentswith Klenow in the presence of dTTP and dCTP. Overhangs may also beconverted to blunt ends by filling in an overhang or removing anoverhang.

Oligonucleotides may be released from the array using a releasable groupor a selectively cleavable portion or linker. The linker may be cleavedby, for example, enzymatic or chemical means. The oligonucleotide may beattached to the solid support via the releasable group so thatactivation or cleavage of the releasable group results in release of theoligonucleotide from the array. See, U.S. patent application Ser. Nos.10/272,155 and 60/434,144. The releasable group may include a moiety orchemical group that is labile, i.e., may be activated or cleaved under agiven set of conditions, but is stable under other sets of conditions. Areversible linker or an enzymatic release mechanism, such as anendonuclease may be used. Release may be mediated by any availablemechanism. Enzymatic methods include, for example, use of anendonuclease or uracil DNA glycosylase (UDG) or (UNG). UNG catalyzes thehydrolysis of DNA that contains deoxyuridine at the site the uridine isincorporated. Incorporation of one or more uridines in theoligonucleotide followed by treatment with UNG will result in release ofthe oligonucleotide from the solid support. Linkers that may be cleavedby chemical means include, for example, disulfide linkers that may bereduced for release, 1,2-diol linkers which may be released by periodatetreatment or a linker that is labile under acidic or basic conditionsmay be used. Releasable linkers may also be activatable by light of acertain wavelength or by exposure to high temperatures. Theoligonucleotide may also have a restriction site incorporated in the 3′region so that the oligonucleotide may be made double stranded on thearray and cleaved with a restriction endonuclease.

C) Methods for Synthesizing Oligonucleotides

Many molecular biology methods employ the use of oligonucleotides. Theymay be used, for example, as probes to detect the presence of asequence, as primers that can be extended by one or more bases, asmodifiable indicators of the presence of a specific ligand, to introducechanges into a sequence of interest, for example, point mutation,insertion of a restriction site or insertion of a priming site, or asanchors that may be used to capture ligands. In many applications poolsof many different oligonucleotides may be used.

When oligonucleotides are synthesized on a solid support a mixture offull-length species and shorter, truncated, capped species may begenerated. For many applications it is desirable to enrich for fulllength species. Methods for enrichment of full length species and forsynthesis of multiple copies of a complementary strand are disclosed.

The synthesized oligonucleotide may contain in the 3′ to 5′ direction acleavable linker, a recognition sequence for a nicking endonuclease, acommon adapter sequence and a specific sequence, for example, a locusspecific sequence. In a preferred embodiment the 5′ end of thesynthesized oligonucleotide is resistant to digestion by a nuclease. Ina particularly preferred embodiment the last 4 bases of the synthesizedoligonucleotide contain a phosphorothioate linkage rather than aphosphodiester linkage. The presence of multiple phosphorothioatelinkages at or near the 5′ end of the synthesized oligonucleotiderenders the oligonucleotide resistant to cleavage by nucleases thatdigest in a 5′ to 3′ direction.

Following synthesis, the synthesized oligonucleotides may be releasedfrom the array into solution using, for example, the cleavable linker. Afirst primer complementary to the 3′ end of the synthesizedoligonucleotides may then be annealed to the released oligonucleotidesand extended. This converts the synthesized oligonucleotides to a doublestranded form. The population may then be treated with an exonuclease.In a preferred embodiment the T7 gene 6 exonuclease is used, this is a5′ to 3′ double strand specific exonuclease. The enzyme is completelyinhibited by four phosphorothioates, Nikiforov et al. (1994) PCR Methodsand Applications 3(5):285-291. This treatment results in digestion ofshorter species which lack the four phosphorothioate bases, leavingprimarily the full length species of synthesized oligonucleotides. Otherexonucleases may also be used, for example, Lambda exonuclease andRecJ_(f).

In a preferred embodiment the remaining oligonucleotides are thenamplified. A primer, which may be the same as the first primer, isannealed to the remaining oligonucleotides and extended. The newlysynthesized strand is nicked by, for example, a nicking enzyme thatrecognized a site in the sequence. Nicking generates a 5′ portion with afree 3′ hydroxyl and a polymerase with strand displacement activity,such as phi29, is used to extend the 5′ portion. The 3′ portion isdisplaced and a new 3′ portion is synthesized in its place. The processof nicking, extension and displacement can be repeated multiple times.Nicking and extension may take place in the same reaction so that whenthe nicking site is regenerated by extension of the 5′ portion it may becleaved and extension may begin again. This allows a linearamplification of the 3′ portion. This portion may contain, for example,a common sequence that may be used as for priming amplification, a locusspecific sequence, and a restriction site. The amplifiedoligonucleotides may be used, for example, in solution based genotypingor for multiplex amplification. For a discussion of genotyping methodsthat use oligonucleotides, see Syvanen, Nature Rev. Gen. 2:930-942(2001).

Cleavage at the nicking site generates a free 3′ hydroxyl in the copystrand which can act as a primer. The primer may then be extended usinga strand displacing polymerase. As the primer is extended it displacesthe remaining copy strand bound to the oligonucleotide. The cleavage andextension reactions are repeated for a plurality of cycles in apreferred embodiment. At each cycle a copy of the 3′ portion of the copystrand (lacking the region that is 5′ of the nicking site) is released.This is complementary to the 3′ portion of the full lengtholigonucleotide.

FIG. 1 illustrates a method to enrich for full length oligonucleotides(103). The oligonucleotides are synthesized, for example, on a solidsupport (100). The oligonucleotides are synthesized so full lengthprobes (103) have a nuclease resistant portion (105) that is not presentin truncated probes (109). After synthesis the oligonucleotides arereleased from the solid support by cleaving a releasable portion (107).After release the oligonucleotides are mixed with a primer (111) that iscomplementary to the 3′ end of the oligonucleotides. The primer isextended, resulting in double stranded oligonucleotides. The doublestranded oligonucleotides are then mixed with a nuclease, for example,T7 gene 6 nuclease which is a 5′ to 3′ exonuclease specific for doublestranded DNA. See, Engler, M. J., and Richardson, C. C, J. Biol. Chem.258, 11197-11205 (1983). Oligonucleotides that lack the nucleaseresistant feature, four phosphorothioate linkages in a preferredembodiment, are digested by the nuclease, while full lengtholigonucleotides are resistant to cleavage and are not digested. Bothstrands of double stranded oligonucleotides that are not full length aredigested and the newly synthesized strand of the double stranded fulllength oligonucleotides is digested. The resulting mixture is enrichedfor single stranded full length oligonucleotides.

In FIG. 2 a method for amplifying the full length oligonucleotides isshown. In this embodiment a template oligonucleotide is synthesized onthe array and the sequence of interest to be produced in large amountsis the complement of the portion of the template oligonucleotide that is5′ of the nicking site. The sample enriched for full lengtholigonucleotides (100) is mixed with at least one primer (102) that iscomplementary to the 3′ end of at least some of the oligonucleotides.The primer is extended generating double stranded oligonucleotides(104). The double stranded oligonucleotides are nicked in the newlysynthesized strand generating a 5′ portion with a free 3′ hydroxyl (106)and a 3′ portion (108). In a preferred embodiment the 3′ portioncontains the sequence or sequences to be amplified. The 5′ portion maythen be extended using, for example, a strand displacing polymerase sothat the 3′ portion is displaced and released. Multiple rounds ofnicking and extension result in release of multiple copies of the 3′portion (110). For example, if the template oligonucleotide synthesizedon the array is 5′ cttgtctggt cccacagttc tccctttagt gagggttaatt*nnnngatcc 3′ (SEQ ID NO: 1) where the site of cleavage at the nickingsite is indicated by * the sequence of interest to be amplified is 5′aattaaccct cactaaaggg agaactgtgg gaccagacaa g 3′ (SEQ ID NO: 2). In apreferred embodiment there are a plurality of different templateoligonucleotides and amplification results in a plurality of differentamplified sequences of interest.

FIG. 3 shows amplification using template oligonucleotide (100).Template oligonucleotides may be synthesized and enriched for fulllength oligonucleotides. A primer that is complementary to the 3′ end ofthe full length oligonucleotides may be hybridized to theoligonucleotide and extended to generate complements of the full lengtholigonucleotides. The complements may then be cleaved at nickingposition (109) thus generating a 5′ portion (101) that can be extended,forming newly synthesized strand (125) and a 3′ portion, the amplifiedsequence (107), that will be displaced when the 5′ portion (101) isextended. In a preferred embodiment the amplified sequence comprises aportion that is common to a plurality of amplified sequences (103) and aportion that is unique to each amplified sequence (105). Multiple roundsof nicking, extension of 101 and displacement of 107 result inamplification, resulting in many copies of the displaced segment (129).

In a preferred embodiment a plurality of different templateoligonucleotides (100) are synthesized and amplification results inamplification of a plurality of different amplified sequences (107).There may be, for example, more than 1,000, 5,000, 10,000, 100,000 or1,000,000 different amplified sequences. In a preferred embodiment aplurality of different amplified sequences each sharing a common primingsite in 103 are synthesized. The sequence 103 may also comprise a tagsequence, a promoter sequence, or a recognition site for a restrictionenzyme. Tag sequences are described in U.S. Pat. No. 6,458,530 and U.S.patent application Ser. No. 09/827,383.

The amplified sequences may be used, for example, for multiplexamplification, for SBE genotype analysis, for OLA genotype analysis, orfor multiplexed anchored runoff amplification (MARA) as described inU.S. patent application Ser. No. 10/272,155. For methods of usingoligonucleotides see, for example, U.S. Pat. Nos. 5,856,092, 6,638,719,5,935,793 and 5,242,794 and U.S. patent application Ser. No. 09/419,817.The amplified sequences may be used, for example, for primer extension,PCR, locus specific amplification, genotyping, isothermal amplification,for reverse transcription of RNA or for RT-PCR. The method may be usedto amplify one sequence or more than one sequence. In preferredembodiments more than 1000, 10,000, 100,000, 1,000,000 or 2,000,000different sequences are amplified.

In one embodiment the oligonucleotides and amplified sequences may beused to amplify genomic fragments. The amplified fragments may then beused, for example, for genotyping by, for example, allele specifichybridization to an array of probes that interrogates genotype. Themethods may be used to synthesize a plurality of oligonucleotides thathave a 3′ locus specific portion and a 5′ portion that comprises anicking site, for example a recognition site for a nicking restrictionenzyme. The locus specific portions may hybridize to a plurality ofpreselected regions in the genome so that amplification with these locusspecific primers results in amplification of fragments of the genomethat contain known polymorphisms. The plurality of oligonucleotides maybe used to amplify genomic fragments in a first round of amplificationand then the fragments may be nicked and amplified using a stranddisplacing DNA polymerase. The amplification may comprise one or moreisothermal steps. See also, U.S. patent application Ser. Nos.60/508,418, 10/318,692, 10/442,021, and 10/681,773.

In a preferred embodiment the amplification is isothermal amplification.The methods employ a nicking step, in which one strand of a doublestranded nucleic acid is cleaved while the other strand is left in tact,and an extension step. The methods preferably employ multiple rounds ofnicking followed by extension of the 3′ hydroxyl generated by thenicking. Nicking may be accomplished by, for example, use of a nickingendonuclease or by use of a restriction enzyme that cleaves bothstrands, but cleavage of one strand is blocked by use of a modifiedbase. In many embodiments a DNA polymerase having strand displacingactivity and lacking 5′-3′ exonuclease activity (such as the DNAPolymerase I Large (Klenow) Fragment or similar enzymes) is used. Seealso U.S. patent application Ser. Nos. 10/318,692 and 60/508,418.

In one embodiment a method to synthesize full length oligonucleotides isdisclosed. Template oligonucleotides are synthesized on a solid supportin a 3′ to 5′ direction. The template oligonucleotides have in the 3′ to5′ direction, a linker region that attaches the oligonucleotide to thesolid support, a primer binding site, a nicking restriction enzymerecognition site and a sequence of interest. The sequence that isamplified is the complement of the 5′ portion of the full lengthtemplate oligonucleotide.

In one embodiment a plurality of oligonucleotides is synthesized on asolid support so that many different oligonucleotide sequences aresynthesized simultaneously. Many copies of ach sequence may besynthesized on the array. There may be, for example, more than 5,000,10,000, 100,000, 500,000, 1 million, or 2.5 million differentoligonucleotide sequences synthesized on a single array, with multiplecopies of each sequence being synthesized. The oligonucleotidessynthesized on the array and enriched for full length sequences may beused, for example, as locus specific primers in a genotyping assay. Inanother embodiment the oligonucleotides synthesized on the array andenriched for full length sequences are subjected to an amplificationstep as described above, so that copies of the complement of the 5′portion of the oligonucleotides may be generated.

Although many of the embodiments described depict release of theoligonucleotides from the array prior to subsequent enrichment andamplification steps, these steps may also be performed while theoligonucleotides are attached to the array. In one embodiment,oligonucleotides are synthesized on a solid support so that full lengtholigonucleotides are resistant to nuclease digestion. Oligonucleotidesthat are not resistant to nuclease digestion are digested with anuclease. In a preferred embodiment the oligonucleotides on the arrayare made double stranded by, for example, hybridization of a primer tothe 3′ portion and extension of the primer. A nuclease that digestsdouble stranded DNA 5′ to 3′, such as T7 gene 6 exonuclease, may beused. After digestion the remaining oligonucleotides may be releasedfrom the array.

In another embodiment oligonucleotides are amplified on an array.Template oligonucleotides are synthesized on an array and made doublestranded. The double stranded oligonucleotide is nicked and the 5′portion of the nicked strand is extended, displacing the 3′ portion ofthe nicked strand. The nicking site is regenerated and can be nickedagain and extended again releasing the 3′ portion again. This cycle ofnicking-extension and release may be repeated for multiple cycles,resulting in amplification of the portion that is 3′ of the nickingsite. This may be done while the template oligonucleotide is attached toa solid support or the template oligonucleotides may be released fromthe solid support prior to amplification. A step for removal oftruncated oligonucleotide species may also be included.

In one embodiment a kit is disclosed. The kit may comprise a pluralityof oligonucleotides comprising in the 5′ to 3′ direction, a locusspecific region that is variable between different oligonucleotides inthe plurality, a first common priming site, a nicking site, and a secondcommon priming site. The oligonucleotides of the kit may be amplifiedaccording to the methods disclosed above to generate amplified nucleicacids complementary the region of the oligonucleotides that is 5′ of therecognition site for the nicking enzyme. The oligonucleotides may befree in solution or attached to a solid support.

EXAMPLE Cleavage of Oligonucleotides from Array Using 1,2-Diol CleavableLinker

Synthesize oligonucleotides on an array including a 1,2-diol linker.Prepare a fresh solution of 10 mM Na Periodate in 100 mM NaOAc pH 6.0 byfirst preparing 50 mM Na Periodate stock solution, 50 mM Na Periodatestock solution is 0.125 g Na Periodate (MW=213.9) in 11.7 ml of 100 mMNaOAc pH 6.0. Dilute this stock solution 1:5 (1 ml 50 mM Na Periodate+4ml 100 mM NaOAc pH 6.0) Inject enough volume to cover array surface(˜200 μl) and incubate at room temperature (25° C.) for 30 minutes.Withdraw solution from array surface and pass over G-25 Sephadex columnto purify nucleic acid sequence.

Enrichment of full-length sequences. Convert single strandoligonucleotides to double-stranded form by mixing 10 μl Water, 2.5 μl10× Taq Gold Buffer, 2 μl 25 mM MgCl₂, 2.5 μl 10× dNTPs, 5 μl 100 μMprimer, 0.25 μl Amplitaq Gold and 2.5 μl cleavage product and incubateat 95° C. for 2 min, 55° C. for 2 min and 72° C. for 6 min, then hold at4° C. Pass the reaction over a G-25 Sephadex column to exchange thebuffer. Add 5 μl of 10× T7 Gene 6 Exonuclease Buffer (USB) (5× buffercontains 200 mM Tris-HCl pH 7.5, 100 mM MgCl₂, 250 mM NaCl). Add 2 μL ofT7 Gene 6 Exonuclease (USB) and incubate at 37° C. for 60 min then holdat 4° C. Pass the reaction over a G-25 Sephadex column to exchange thebuffer.

Amplification of Full-Length Enriched Oligonucleotides

Convert enriched single strand oligonucleotides to double-stranded formas described above. Mix 21.2 μL Water, 3 μL 10×DNA pol I Large Fragment(Klenow) Buffer, 0.35 μM NaCl, 3 μL 10× dNTPs, 0.5 μL double strandedenriched oligo, 1 μL N. Alw I (NEB), and 1 μL Klenow (NEB). Incubate at37° C. for 6 hours to overnight. Check aliquot of reaction on 10%, 15%,or 20% Denaturing (8 M urea) acrylamide Gel. Pass the reaction over aG-25 Sephadex column to exchange the buffer.

CONCLUSION

It is to be understood that the above description is intended to beillustrative and not restrictive. Many variations of the invention willbe apparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. All cited references,including patent and non-patent literature, are incorporated herewith byreference in their entireties for all purposes.

I claim:
 1. A method of making a plurality of single strandedoligonucleotides, which comprises: synthesizing a plurality of singlestranded oligonucleotides on a solid support, wherein the plurality ofsingle stranded oligonucleotides comprises a plurality of full lengtholigonucleotides and at least one truncated oligonucleotide, wherein thefull length oligonucleotides comprise at least one terminalphosphorothioate linkage, and wherein the at least one terminalphosphorothioate linkage confers exonuclease resistance to the fulllength oligonucleotides; and digesting the at least one truncatedoligonucleotide with an exonuclease, wherein the exonuclease is capableof digesting single stranded oligonucleotides.
 2. The method of claim 1,additionally comprising: releasing the full length oligonucleotides fromthe solid support by cleaving a cleavable portion of theoligonucleotides.
 3. The method of claim 2, wherein the cleavableportion comprises uracil.
 4. The method of claim 3, wherein uracil DNAglycosylase is used to generate an abasic site and the full lengtholigonucleotides are released by cleavage at the abasic site.
 5. Themethod of claim 1, wherein the full length oligonucleotides comprise atleast four terminal phosphorothioate linkages.
 6. The method of claim 1,wherein the exonuclease cleaves 5′ to 3′.
 7. The method of claim 6,wherein the exonuclease is a RecJ_(f) exonuclease.
 8. The method ofclaim 1, wherein the full length oligonucleotides comprise an adaptorsequence.
 9. The method of claim 8, wherein the adaptor sequencecomprises a primer binding site.
 10. The method of claim 8, wherein theadaptor sequence comprises a recognition site for an endonuclease. 11.The method of claim 1, wherein the plurality of full lengtholigonucleotides comprises at least 1000 different sequences.
 12. Themethod of claim 1, wherein the synthesis strategy for theoligonucleotides is combinatorial masking.
 13. A method of making aplurality of single stranded oligonucleotides, comprising: synthesizinga plurality of single stranded oligonucleotides on a solid support,wherein the single stranded oligonucleotides are synthesized on thesolid support in a 3′ to 5′ direction, wherein each single strandedoligonucleotide comprises, in the 3′ to 5′ direction, a cleavableportion, an adaptor sequence, a sequence of interest, and a 5′ end thatcomprises at least one terminal phosphorothioate linkage, and whereinthe at least one terminal phosphorothioate linkage confers exonucleaseresistance to the 5′ end.
 14. The method of claim 13, wherein the 5′ endof the single stranded oligonucleotides comprises at least four terminalphosphorothioate linkages.
 15. The method of claim 13, wherein thecleavable portion comprises uracil.
 16. The method of claim 13, whereinthe adaptor sequence comprises a primer binding site.
 17. The method ofclaim 13, wherein the adaptor sequence comprises a recognition site foran endonuclease.
 18. The method of claim 13, wherein the plurality ofsingle stranded oligonucleotides on the solid support comprises at least1000 different sequences.
 19. The method of claim 13, wherein thesynthesis strategy for the single stranded oligonucleotides iscombinatorial masking.
 20. A synthesized single strandedoligonucleotide, comprising in the 3′ to 5′ direction: a cleavableportion comprising uracil, an adaptor sequence, a sequence of interest,and a 5′ end that comprises at least one terminal phosphorothioatelinkage, wherein the at least one terminal phosphorothioate linkage isdesigned to confer exonuclease resistance to the 5′ end, wherein theadaptor sequence comprises a recognition site for an endonuclease. 21.The single stranded oligonucleotide of claim 20, wherein the 5′ endcomprises at least four terminal phosphorothioate linkages.
 22. Thesingle stranded oligonucleotide of claim 20, wherein the adaptorsequence comprises a primer binding site.
 23. The single strandedoligonucleotide of claim 20, wherein the oligonucleotide is synthesizedby combinatorial masking.